Projecting device for displaying electrical images

ABSTRACT

A projecting device for displaying electrical images. The projecting device has an illumination device for emitting a polarized trichrome light, three modulating devices for modulating three polarized monochrome lights to display the same electrical image, a light separating device having a first dichroic mirror and a third polarization beam splitting mirror arranged along a first diagonal direction and a first and a second polarization beam splitting mirrors arranged along a second diagonal direction, and a first retarder film installed between the second and the third polarization beam splitting mirrors. The first dichroic mirror, the first and second polarization beam splitting mirrors are used for separating the polarized trichrome light into three monochrome lights and passing each monochrome light to a correspondent modulating device for optical modulation. The three modulated lights reflected from the three modulating devices are transmitted to the third polarization beam splitting mirror and synthesized into an output light beam for displaying the electrical image.

BACKGROUND OF INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a projecting device, and morespecifically, to a projecting device for displaying electrical images.

[0003] 2. Description of the Prior Art

[0004] Please refer to FIG. 1. Fi_Hlt493057585g_Hlt493057585.1 is aperspective view of a prior art projecting device 10 of an LCDprojector. The projecting device 10 comprises a light source 12 thatproduces a white light beam, a uniform illumination optical device 14installed in front of the light source 12 for converging the white lightemitted from the light source 12 into a uniformly distributedrectangular light beam, a light separating device 16 for separating therectangular light beam into red, green and blue color input light beams,a trichromic prism 18 having three input sides and an output side forsynthesizing the three input light beams into an output light beam,three modulating panels 20 each formed by a monochrome liquid crystalpanel and separately installed in front of the three input sides of thetrichromic prism 18 for modulating the three input light beams, threefocusing lenses 17, 19 and 21 separately installed in front of the threemodulating panels 20 for focusing the three input light beams from thelight separating device 16 onto the three modulating panels 20, and aprojecting lens 22 installed in front of the output side of thetrichromic prism 18 for projecting the synthesized output light beamfrom the trichromic prism 18 onto a screen 24. Each of the modulatingpanels 20 is formed by a transparent monochrome liquid crystal panel fordisplaying a monochrome image. The trichromic prism 18 synthesizes thethree monochrome images to form the output color image.

[0005] The light separating device 16 comprises a first dichroic mirror26 for separating the red light from the rectangular light beam, areflecting mirror 27 for reflecting the red light from the firstdichroic mirror 26 onto the focusing lens 17, a second dichroic mirror28 for separating light reflected from the first dichroic mirror 26 byreflecting blue light to the focusing lens 19, and two optical lenses 30and two reflecting mirrors 32 for passing and reflecting green light tothe focusing lens 21. FIG. 1 clearly shows that the distance traveled bythe green light is much longer than that of the red and blue lights.Since traveling distances affect light intensities, the two opticallenses 30 installed in front of the two reflecting mirrors 32 areessential to converge the green light so as to compensate for the lossof its light intensity.

[0006] However, the installation of the two optical lenses 30 makes astructure of the light separating device 16 complicated and costly. Itis therefore an important objective to provide a projecting device witha simple structure that can solve the problem of unequal travelingdistances for the three color beams.

SUMMARY OF INVENTION

[0007] It is therefore a primary objective of the present invention toprovide a projecting device to solve the above mentioned problem.

[0008] Briefly, in a preferred embodiment, the present inventionprovides a projecting device comprising:

[0009] an illumination device for emitting a polarized trichrome lightcomprising three primary colors with various polarization;

[0010] a first, second and third modulating device, each modulating,reflecting, and changing the polarization of its own distinct polarizedmonochrome light;

[0011] a light separating device having a first dichroic mirror, a firstpolarization beam splitting mirror, a second polarization beam splittingmirror, and a third polarization beam splitting mirror, the firstdichroic mirror and the third polarization beam splitting mirror beingarranged along a first diagonal direction, and the first and the secongpolarization beam splitting mirrors being arranged along a seconddiagonal direction perpendicular to the first diagonal direction; and

[0012] a first retarder film installed between the second and the thirdpolarization beam splitting mirrors; wherein the first dichroic mirrorseparates the polarized trichrome light into a first polarizedmonochrome light and a polarized dichrome light, and transmits these twolights separately to the first and second polarization beam splittingmirror, the first polarization beam splitting mirror transmits the firstpolarized monochrome light to the first modulating device and transmitsthe modulated light reflected from the first modulating device to thethird polarization beam splitting mirror, the second polarization beamsplitting mirror separates the polarized dichrome light into second andthird polarized monochrome lights which are directly transmitted to thesecond and third modulating devices, and then transmits the modulatedlights reflected from the second and third modulating devices to thethird polarization beam splitting mirror through the first retarderfilm, and the first retarder film changes the polarization of one of themodulated lights reflected from the second and third modulating devices,the modulated lights transmitted from the first and second polarizationbeam splitting mirrors are synthesized by the third polarization beamsplitting mirror to form an output light beam.

[0013] It is an advantage of the present invention that the projectingdevice has a very simple structure.

[0014] It is another advantage of the present invention that thetraveling distances of the three polarized light beams are approximatelyequal and shorter than that of the prior art device.

[0015] These and other objects and the advantages of the presentinvention will no doubt become obvious to those of ordinary skill in theart after having read the following detailed description of thepreferred embodiment that is illustrated in the various figures anddrawings.

BRIEF DESCRIPTION OF DRAWINGS

[0016]FIG. 1 is a perspective view of a prior art projecting device ofan LCD projector.

[0017] FIG_Hlt493057594._Hlt4930575942 is a perspective view of aprojecting device of an LCD projector according to the presentinvention.

[0018] FIG_Hlt493057598._Hlt4930575983 is a schematic diagram of thedichroic-polarization beam splitter prism of the present invention.

[0019] Fi_Hlt493057601g_Hlt493057601.4 is a schematic diagram of themodulation apparatus of the present invention.

[0020] FIG._Hlt4930576045_Hlt493057604 is a schematic diagram of theillumination device of the projecting device of an LCD projector shownin FIG. 2.

[0021] F_Hlt493057607i_Hlt493057607gs.6 and 7 are schematic diagrams ofthe alternative light separating device and projecting device of an LCDprojector, respectively, according to the present invention.

DETAILED DESCRIPTION

[0022] Please refer to FIGS. 2 to 4. FIG. 2 is a perspective view of aprojecting device 40 of an LCD projector according to the presentinvention. FIG. 3 is a schematic diagram of the dichroic-polarizationbeam splitter prism 50 of the present invention. FIG. 4 is a schematicdiagram of the modulation apparatus 44 of the present invention. Theprojecting device 40 comprises an illumination device 42, threemodulating devices 44, 46 and 48, a dichroic-polarization beam splitterprism 50 and a projecting lens 52. The illumination device 42 emits auniformly distributed approximately white light beam which comprisesred, green and blue colors, each with distinct polarizations. Forexample, the illumination device 42 of the present invention emits apolarized light comprising red R, green G* and blue B polarized lightswherein the polarization of the green G* polarized light is differentfrom the other polarized lights R and B. The three modulating devices44, 46 and 48 are used for modulating and shifting the polarization ofthe three polarized monochrome lights by utilizing a method involvingreflection of light. The dichroic-polarization beam splitter prism 50receives and sends the three polarized lights R, G* and B to the threecorresponding modulating devices 44, 46, and 48 where each polarizedlight undergoes processing, modulation, and change in polarization withsynthesizing of the three polarized monochrome lights and formation ofan output light beam. The projecting lens 52 is installed in front ofthe output side of the dichroic-polarization beam splitter prism 50 forprojecting the output light beam synthesized by the three polarizedmonochrome lights and emitted from the output side of thedichroic-polarization beam splitter prism 50 to a screen 54.

[0023] The dichroic-polarization beam splitter prism 50 comprises fivetriangular prisms 60A, 60B, 60C, 60D, 60E, each having a thin reflectivecoating on their interfaces. The dichroic-polarization beam splitterprism 50 further comprises a first dichroic mirror 62 and a thirdpolarization beam splitting mirror 64 installed within thedichroic-polarization beam splitter prism 50 along the first diagonalline and the first polarization beam splitting mirror 66 and secondpolarization beam splitting mirror 68 are also installed within thedichroic-polarization beam splitter prism 50 along the second diagonalline perpendicular to the first and second dichroic mirrors. Thedichroic-polarization beam splitter prism 50 further comprises a firstretarder film 70 installed between the second and the third polarizationbeam splitting mirrors 68, 64.

[0024] Each of the three modulating devices 44, 46 and 48 comprises amirror-type light modulator 76 for modulating and reflecting an incidentlight to generate a modulated light, and a quarter-wave retarder 78 forretarding both the incident light and modulated light by a quarter of awavelength so that the incident light of the modulating device and themodulated light generated by the modulating device have oppositepolarizations. The mirror-type optical modulator 76 can be a digitalmicro-mirror device or a mirror-type liquid crystal display.

[0025] As shown in FIG. 2, after the polarized trichrome light emittedfrom the illumination device 42 enters the dichroic-polarization beamsplitter prism 50, it is separated by the first dichroic mirror 62 intoa first blue polarized monochrome light B and a polarized dichrome lightconsisting of a red polarized light R and green polarized light G*. Theblue polarized light B is reflected by the first dichroic mirror 62 andtherefore transmitted to the first polarization beam splitting mirror66. The red polarized light R and green polarized light G* lightpenetrate through the first dichroic mirror 62 and is thereforetransmitted to the second polarization beam splitting mirror 68. Thefirst polarization beam splitting mirror 66 has a special coating andcan reflect a S-STATE polarized light and pass an P-STATE polarizedlight. Thus, the blue polarized light B is transmitted by the firstpolarization beam splitting mirror 66 to the first modulating device 48which forms and reflects a modulated light B* which is transmitted bythe first polarization beam splitting mirror 66 to the thirdpolarization beam splitting mirror 64. The second polarization beamsplitting mirror 68 passes S-STATE polarized light and reflects P-STATEpolarized light so that the red polarized light R is reflected to thesecond modulating device 44 where it is modulated into red polarizedlight R* and the green polarized light G* is transmitted to the thirdmodulating device 46 where it is modulated into green polarized light G.Both modulated lights (R* & G) are transmitted by the secondpolarization beam splitting mirror 68 to the first retarder film 70. Thefirst retarder film 70 will change the polarization of the red light butnot the green light. Thus, after passing through the first retarder film70, the modulated light R* will becomes R, and the modulated light Gwill be still G. Finally, the third polarization beam splitting mirror64 will pass the blue polarized light B* and reflect the red polarizedlight R and green polarized light G into the projecting lens 52 to forma synthesized polarized trichrome light B*GR which is projected onto thescreen 54. The simple structure of the projecting device 40 of thepresent invention uses the dichroic-polarization beam splitter prism 50to separate and synthesize the trichrome light beam where the travelingdistances for each of the polarized light beams are approximately equaland shorter than the distances of the input light beams of the prior artprojecting device 10.

[0026] The dichroic-polarization beam splitter prism 50 uses a set ofone dichroic mirrors 62 and three polarization beam splitting mirrors66, 68, 64 to separate and individually modulate the three polarizedlights. Therefore, the illumination device 42 must provide thedichroic-polarization beam splitter prism 50 with a polarized trichromelight comprising a polarized monochrome light and a dichroic polarizedlight with a different polarization for final output of a perfectlysynthesized trichrome light beam.

[0027] Please refer to FIG. 5. FIG. 5 is a schematic diagram of theillumination device 42 of the projecting device 40 of an LCD projector.The illumination device 42 comprises a light source 80 for generating atrichrome unpolarized light RR*GG*BB* which comprises red, green andblue lights, a light polarizing device 82 for transforming the trichromeunpolarized light RR*GG*BB* into a polarized trichrome light RGB, and alight separating device 84 for separating the polarized trichrome lightRGB into a green polarized light G and a polarized dichrome light RB.The light separating device 84 further comprises two dichroic mirrors86, 88 for separating the green polarized light G from the polarizedtrichrome light RGB and synthesizing the green polarized light G* into apolarized trichrome light RG*B, two reflecting mirrors 90, 92 forreflecting the green polarized light G and the polarized dichrome lightRB, and a half-wave retarder 94 for retarding and modulating the greenpolarized light G into the green polarized light G*. As shown in FIG. 2,the illumination device 42 outputs a polarized trichrome light RG*B tothe first dichroic mirror 62 of the dichroic-polarization beam splitterprism 50.

[0028] Please refer to FIG. 6 and FIG. 7. FIGS. 6 and 7 representschematic diagrams of an alternative light separating device 100 and aprojecting device 110 of an LCD projector, respectively, according tothe present invention. The light separating device 100 has a far simplerstructure than the previously described light separating device 84 andcomprises a dichroic mirror 102, two reflecting mirrors 104 and 106, anda half-wave retarder 108. The output orientation of the green polarizedlight G* is perpendicular to that of the polarized dichrome light RB.Unlike the previously described dichroic mirror 62, the dichroic mirror112 shown in F_Hlt503168810i_Hlt503168810g. 7 is coated to reflect boththe green polarized light G* and the blue polarized light B whilepassing the red polarized light R.

[0029] Additionally, in this embodiment, the first retarder film 70shown in FIG. 2 changes the polarization of the red light but not thegreen one. However, a retarder film which can change the polarization ofthe green light but not the red one can also be used to replace thefirst retarder film 70 if an alternative retarder film is installedbetween the first and the third polarization beam splitting mirrors 66,64. In this manner, the polarization of the blue light (B) reaching thethird polarization beam splitting mirror 64 is different from thepolarization of the red and green lights (R*, G*). The thirdpolarization beam splitting mirror 64 will reflect the polarized light Band pass the polarized lights R*, G* to form a synthesized polarizedtrichrome light BG*R* which is projected onto the screen 54.

[0030] From the foregoing, it is clear that the projecting devices 40and 110 of the present invention are simple in structure and provideapproximately equal light traveling distances that are shorter than thatof the prior art device projecting device 10. Thus, special opticallenses to compensate for the loss of light intensity are not needed inprojecting devices 40 and 110 thereby simplifying the structure,lowering manufacturing costs, and improving image quality.

[0031] Those skilled in the art will readily observe that numerousmodifications and alterations of the propeller may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A projecting device comprising: an illuminationdevice for emitting a polarized trichrome light which comprises red,green and blue lights; three modulating devices defined as first ,second, and third modulating devices, each of the modulating devicesbeing used for reflecting a polarized monochrome light to modulate itand change its polarization; a light separating device having a firstdichroic mirror, a first polarization beam splitting mirror, a secondpolarization beam splitting mirror, and a third polarization beamsplitting mirror, the first dichroic mirror and the third polarizationbeam splitting mirror being arranged along a first diagonal direction,and the first and the secong polarization beam splitting mirrors beingarranged along a second diagonal direction perpendicular to the firstdiagonal direction; and a first retarder film installed between thesecond and the third polarization beam splitting mirrors; wherein thefirst dichroic mirror transfers the polarized trichrome light into afirst polarized monochrome light and a polarized dichrome light, andtransmits these two lights separately to the first and secondpolarization beam splitting mirror, the first polarization beamsplitting mirror transmits the first polarized monochrome light to thefirst modulating device and transmits the modulated light reflected fromthe first modulating device to the third polarization beam splittingmirror, the second polarization beam splitting mirror separates thepolarized dichrome light into second and third polarized monochromelights which are directly transmitted to the second and third modulatingdevices, and then transmits the modulated lights reflected from thesecond and third modulating devices to the third polarization beamsplitting mirror through the first retarder film, and the first retarderfilm changes the polarization of one of the modulated lights reflectedfrom the second and third modulating devices, the modulated lightstransmitted from the first and second polarization beam splittingmirrors are synthesized by the third polarization beam splitting mirrorto form an output light beam.
 2. The projecting device of claim 1further comprising a projecting lens for projecting the output lightbeam from the third polarization beam splitting mirror onto a screen. 3.The projecting device of claim 1 wherein the light separating device isa rectangular trichromatic prism having a first diagonal line and asecond diagonal line perpendicular to each other, wherein the firstdichroic mirrors and the third polarization beam splitting mirror areinstalled inside the trichromatic prism along the first diagonal line,and the first and second polarization beam splitting mirrors are alsoinstalled inside the trichromatic prism along the second diagonal line.4. The projecting device of claim 1 wherein the polarized trichromelight emitted from the illumination device comprises a polarizedmonochrome light and a polarized dichrome light which are transmitted tothe first dichroic mirror from the opposing sides of the first dichroicmirror.
 5. The projecting device of claim 1 wherein the polarizedtrichrome light emitted from the illumination device is a single lightbeam which is directly transmitted to the first dichroic mirror.
 6. Theprojecting device of claim 1 wherein the first polarization beamsplitting mirror reflects the first monochrome light to the firstmodulating device, and then the modulated light reflected from the firstmodulating device is transmitted through the first polarization beamsplitting mirror and passed to the third polarization beam splittingmirror.
 7. The projecting device of claim 1 wherein the first monochromelight is transmitted through the first polarization beam splittingmirror and passed to the first modulating device, and then the modulatedlight reflected from the first modulating device is reflected to thethird polarization beam splitting mirror by the first polarization beamsplitting mirror.
 8. The projecting device of claim 1 wherein the secondpolarized monochrome light is reflected to the second modulating deviceby the second polarization beam splitting mirror and the third polarizedmonochrome light is transmitted to the third modulating device bytransmitting through the second polarization beam splitting mirror, themodulated light reflected from the second modulating device istransmitted to the third polarization beam splitting mirror bytransmitting through the second polarization beam splitting mirror, andthe modulated light reflected from the third modulating device isreflected to the third polarization beam splitting mirror by the secondpolarization beam splitting mirror.
 9. The projecting device of claim 1wherein each of the modulating devices comprises a mirror-type opticalmodulator for modulating an incident light to generate a modulatedlight, and a quarter-wave retarder for retarding both the incident lightand the modulated light by a quarter wavelength so that the incidentlight of the modulating device and the modulated light generated by themodulating device have opposite polarizations.
 10. The projecting deviceof claim 9 wherein the optical modulator is a digital micro-mirrordevice.
 11. The projecting device of claim 9 wherein the opticalmodulator is a liquid crystal display panel.
 12. The projecting deviceof claim 1 wherein the illumination device comprises a light source forgenerating a trichrome unpolarized light which comprises red, green andblue lights, a light polarizing device for converting the trichromeunpolarized light into a polarized trichrome light, a light separatingdevice for separating the polarized trichrome light into a monochromelight and a dichrome light, and a retarder for changing the polarizationof the monochrome light or dichrome light to generate the trichromelight of various polarizations.